Definitions #
- Cellulitis: bacterial infection of the skin and soft tissue that can affect the epidermis, dermis, hypodermis and superficial fascia1
- Erysipelas: superficial, more commonly occurring in children and characterised with raised and sharply demarcated inflammation, with clear margins differentiating from uninvolved skin2
- Folliculitis: localised inflammation of a hair follicle or sebaceous glands, limited to the epidermis4
- Furuncles: deep folliculitis beyond the dermis with abscess formation in the subcutaneous tissue4
Carbuncles: confluent folliculitis, forming an inflammatory mass; abscess and skin necrosis may be present4
Key Points #
- Antibiotics are not needed in young, healthy patients with uncomplicated cellulitis
- In the more at-risk population, antibiotics, leg elevation and rest are generally sufficient to treat most cellulitis
- Have a high index of suspicion for necrotising fasciitis in patients who have haemodynamic instability, pain out of proportion to appearance, dusky skin and hard subcutaneous tissue with crepitus on palpation
- In necrotising fasciitis, the cornerstones of management are early commencement of antibiotic therapy while preparing for urgent surgical debridement.
Triage #
If uncomplicated cellulitis: Attend within hours
If complicated cellulitis: Attend within 30 minutes and refer for review by senior clinician and refer to general surgery for expert advice.necrotising soft tissue infection/necrotising fasciitis, or Fournier’s gangrene, or orbital cellulitis or when the patient is hemodynamically unstable secondary to sepsis
Causes #
The following are distinct diagnostic features and common presentations for the respective organisms however are not definitive causes(3).
Non-purulent
- Streptococcus species (eg group B, C or G)
Purulent
- Staphylococcus aureus
Exposure specific
Penetrating trauma or ulceration
- Staphylococcus aureus
Fresh water exposure
- Aeromonas species
Salt water exposure
- Vibrio species
Clinical features #
Red Flags
Necrotising soft tissue infection/Necrotising fasciitis:
- Rapid onset and progression
- Severe pain out of proportion to appearance
- Skin duskiness/discolouration
- Numbness
- Hard subcutaneous tissue that extends beyond superficial involvement
- Subcutaneous crepitus
- Haemodynamic instability
- High fever, disorientation 2
- Delirium could also be secondary to simple cellulitis in the elderly population
Fournier’s gangrene: necrotising fasciitis of the external genitalia that can spread rapidly to the anterior abdominal wall and gluteal muscles1
Orbital cellulitis: External eye muscle ophthalmoplegia and proptosis, decreased visual acuity and chemosis, blurred or double vision2
Most common
- Redness; can be well-demarcated or generalised
- Mark area of redness/take daily photos to monitor progression
- Beware that cellulitis will usually worsen in the first 102 days before improving
- Swelling
- Heat
- Tenderness
- Blistering
Systemic:
- Fever/malaise
- Unilateral involvement
- Lymphadenopathy
Further history to assess risk factors2
- Venous insufficiency
- Diabetes mellitus
- Immunosuppression
- Chronic kidney disease
- Obesity
- Eczema
- Foreign body/trauma
Investigations #
Initial investigations2
| Investigation | Significance |
| FBE | Elevated WCC suggests infection |
| CRP | Elevated CRP represents inflammation (note delayed response) |
| UEC/LFT | AKI secondary to shock indicates end organ damage and will also influence antibiotic choice |
Further investigations2
| Investigation | Indication |
| Wound MCS | Signs of broken skin and discharge present, worsening infection, poor healing/not healing as expected and recurring infection Cultures and sensitivities will determine antibiotic choice |
| Blood cultures | Bacteraemia suspected Positive cultures indicate bacteraemia (can occur secondary to cellulitis) |
| Soft tissue ultrasound* | Suspected foreign body at site of infectionSuspected complex abscess (perianal abscesses, polymicrobial or resistant pathogens), necrotising fasciitis Assessment of size/extent of abscess |
| X-ray | Evaluation of osteomyelitis in prolonged cellulitis or long-standing non-healing ulcers |
| CT/MRI* | Usually only necessary for complex skin abscesses and associated complications (osteomyelitis, necrotising fasciitis) |
(*) indicates discussion with senior clinician
Referrals
| General surgery/ Plastics (depending on hospital) | Consider referral if signs of skin abscesses, recurrent skin abscesses, complex abscesses, increased risk of complications or necrotising skin infection |
| Infectious diseases | Consider referral if polymicrobial cellulitis present |
Differential Diagnosis #
- Deep venous thrombosis
- Stasis dermatitis
- Superficial thrombophlebitis
- Drug reactions
- Insect bites
- Vasculitis
- Acute gout
Management #
Cellulitis with haemodynamic instability5
Call out box on haemodynamic instability: systemic features with lactic acidosis and sBP<90mmHg (septic shock if not responsive to fluid resuscitation)
If necrotising skin and soft tissue is suspected, surgical debridement of devitalised tissue and urgent antibiotic therapy are essential; refer to general surgery/plastics.
Meropenem 1 g IV, 8 hourly OR Piperacillin + tazobactam 4+0.5 g IV, 6 hourly
PLUS
Vancomycin 25 to 30 mg/kg IV, as a loading dose (link to vancomycin dosing page)
PLUS
Clindamycin 600 mg IV, 8 hourly OR Lincomycin 600 mg IV, 8 hourly
If infection is associated with a wound that has been immersed in water, ciprofloxacin is included in the empirical regimen, because Aeromonas isolates often produce carbapenemase enzymes.
A total duration of two weeks of therapy (oral + IV) is recommended.
Cellulitis with systemic features3
Call out box on systemic features: Two or more of the following: T >38°C OR <36°C, HR >90bpm, RR>20 breaths/minute, WCC>12 OR <4 but not associated haemodynamic instability (hypotension, septic shock or rapid progression of systemic features)
Erysipelas or non-purulent (S. pygenes suspected)
Benzylpenicillin 1.2 g IV, 6 hourly
Purulent (Staphylococcus aureus suspected)
Flucloxacillin 2 g IV, 6 hourly
MRSA suspected
Vancomycin IV (link to vancomycin dosing page)
OR
Clindamycin 600 mg IV, 8 hourly
OR
Lincomycin 600 mg IV, 8 hourly
Cellulitis without systemic features3
Erysipelas or non-purulent (S. pygenes suspected)
Phenoxymethylpenicillin 500 mg orally, 6 hourly for 5 days
OR
Procaine benzylpenicillin 1.5 g IM, daily for at least 3 days
Purulent (Staphylococcus aureus suspected)
Dicloxacillin 500 mg orally, 6 hourly for 5 days
OR
Flucloxacillin 500 mg orally, 6 hourly for 5 days
OR
Cefalexin 500 mg orally, 6 hourly for 5 days
liquid formulation is better tolerated in the paediatric population
MRSA suspected
Trimethoprim + sulfamethoxazole 160+800 mg orally, 12 hourly for 5 days
OR
Clindamycin 450 mg orally, 8 hourly for 5 days
References #
- Amboss [Internet]. [place unknown]; publisher unknown]; Amboss; 2021. Skin and soft tissue infections; 2021 [cited 2021 Aug 29]; Available from: https://www.amboss.com/us/knowledge/Skin_and_soft_tissue_infections/
- BMJ Best Practice. Cellulitis and Erysipelas [Internet]. England and Wales; BMJ Publishing Group Limited; 2021 [last updated 2021 Jun 18; cited 2021 Aug 29], Available from: https://bestpractice.bmj.com.acs.hcn.com.au/topics/en-gb/3000172?q=Cellulitis%20and%20erysipelas&c=recentlyviewed
- eTG complete [Internet]. Melbourne (Vic): Therapeutic Guidelines Ltd; 2019. Cellulitis and erysipelas [last updated 2021 Aug; cited 2021 Aug 29], Available from: https://tgldcdp.tg.org.au.acs.hcn.com.au/viewTopic?topicfile=cellulitis-erysipelas&guidelineName=Antibiotic&topicNavigation=navigateTopic#toc_d1e460
- Stevens DL, Bisno AL, Chambers HF, et al. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America. Clinical Infectious Diseases. 2014 July 15; 59(2): e10–e52
- eTG complete [Internet]. Melbourne (Vic): Therapeutic Guidelines Ltd; 2019. Necrotising skin and soft tissue infections [last updated 2019 April; cited 2021 Aug 29], Available from: https://tgldcdp.tg.org.au.acs.hcn.com.au/viewTopic?topicfile=skin-soft-tissue-necrotising-infections§ionId=abg16-c136-s3#toc_d1e143
Contributors
Reviewing Consultant/Senior Registrar
Dr Aashima Juneja
Dr Anita Ng
